nfp: bpf: rename map_lookup_stack() to map_call_stack_common()

We will reuse most of map call code gen for other map calls.
Rename the lookup gen function and use meta->func_id instead
of hard-coding lookup.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Quentin Monnet <quentin.monnet@netronome.com>
Reviewed-by: Jiong Wang <jiong.wang@netronome.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>